This invention relates generally to the generation of intense coherent radiation in various applications, such as high gradient radio frequency accelerators and high-power radar installations. More particularly, the present invention relates to the generation of amplified microwave energy by means of a klystron type of amplifier device.
The use of a klystron amplifier within which microwave energy interacts with beam electrons is generally well known in the art, as disclosed for example in U.S. Pat. Nos. 3,274,430, 4,820,996 and 5,162,747 to EL-Hefini, Heppinstall et al. and Tammaru, respectively. U.S. Pat. No. 5,142,250 to Uhm et al. on the other hand, relates to the interaction of an electron beam with a body of plasma before it is fed to a klystron amplifier utilized as a high-power microwave generator. As to the generation of plasma itself, U.S. Pat. Nos. 3,232,046 and 5,051,659 to Meyer and Uhm et al. are of interest.
In a Klystron amplifier, the beam generated by an electron gun is propagated through a drift tube extending between input and output resonator cavities for interaction with the microwave energy thereat. Such resonator cavities respectively induce bunching or density modulation of the electrons in the beam along the drift tube and delivery of RF power by charge collection from the beam at a resonator cavity tuned to the excitation frequency of the microwave energy introduced to the input cavity. In such prior art klystron amplifiers, the cavity size and opening is inversely related to excitation frequency so that cavity size must be dimensionally reduced in order to increase excitation frequency. Resonator cavities of reduced size, however, create various problems such as shorting and electron emission at cavity gap openings where the interaction between beam electron and high-power microwave energy occurs. Prior efforts to enhance operation of high-power klystron amplifiers, involved use of plural intermediate cavities between the input and output cavities as disclosed for example in the EL-Hefini patent aforementioned. Such arrangements for enhancing high-power operation not only increase the drift space length in the klystron amplifier, but are inconsistent with its operation under high excitation frequencies. Accordingly, a major problem with the use of a relativistic klyston amplifier resides in its inability to simultaneously accommodate both high-power and high frequency operations with an acceptable degree of overall efficiency.
It is therefore an important object of the present invention to provide a klystron amplifier arrangement through which the efficiency of current modulation of an electron beam may be simultaneously enhanced with respect to high power and high frequency operation.
A further object of the invention in accordance with the foregoing objective is to provide a more efficient klystron amplifier device having a relatively short length drift space between cavities.